When the TARDIS lands on an arid planet, it seems as though the whole place is desolate and lifeless. But then the Doctor, Steven and Vicki discover two crashed space ships: one contains the Drahvins, a race of stunning beauty, the other contains the hideous Rills. However, as the team soon finds out, appearances can be deceptive. It emerges that the beauty of the Drahvins hides a colony of mindless clones who are controlled by the cruel, powerful Maaga, whereas the ugly Rills are friendly and intelligent explorers.